1. Field of the Invention
This invention relates to mechanical switches for closing and opening electrical circuits. The switches may be set in a closed position for any desired period of time and then reset to an open position. More particularly the invention relates to gas operated conductive fluid switching devices for controlling the flow of current in electrical circuits.
2. Description of the Prior Art
Conductive fluid switching devices which are gas operated have been known for many years. These devices take various forms but each generally includes a capillary tube connected to one or more gas-filled bulbs having a diameter considerably larger than the diameter of the capillary tube. The gas in the gas-filled bulb is heated to provide pressure from one end of the capillary tube to urge the conductive fluid, generally mercury, toward the other end of the capillary tube.
U.S. Pat. No. 310,472 discloses an electrical switch including an enclosed glass tube having a pair of chamber sections united by a capillary passage containing a globule of mercury in which two wires, which may be made of platinum, are terminated. An electrical current producing heat expands the gas in the chamber forcing the globule of mercury through the capillary passage to control the operation of the switch. The heat may be generated by an electrical circuit within or outside of the chamber. U.S. Pat. No. 1,598,874 describes a switch comprising a closed container in which electrodes are sealed and at appropriate times brought into electrical conducting relation with one another through the agency of a body of highly pure mercury likewise contained in the container. The container may be filled with an inert gas such as nitrogen, helium or hydrogen. The electrodes may be made from the iron group, such as, iron, nickel and tungsten. U.S. Pat. No. 2,012,491 discloses a switch comprising a pair of hydrogen-filled chamber sections connected by a tubular section containing mercury. A heating element is disposed in each chamber section. The switch is operated as a latch by selectively immersing in the mercury first or second contacts depending upon which of the two heating elements is energized to expand the gas in its associated chamber section. U.S. Pat. No. 2,666,105 discloses a switch comprising a capillary tube coupled between two gasfilled chamber sections. Within the tube is a globule of mercury and a pair of wires contactable by the mercury. Heat produced in either of the two chamber sections alternately opens and closes the switch. In an embodiment of this switch, elongated metal bulbs of cylindrical shape are attached to the capillary tube and communicate therewith through a pair of spherical enlarged openings used to protect the metal from the mercury. U.S. Pat. No. 3,102,179 describes a switch comprising a capillary tube and a globule of mercury wherein a pair of stoppers are disposed within opposite ends of the capillary tube so as to prevent mercury from flowing out of the tube while providing passage of gas to the mercury. A wire and a glass thread are suggested as embodiments of the stopper. U.S. Pat. No. 3,176,101 discloses a switch comprising a capillary tube coupled between two gas-filled bulb-type chamber sections. Within the tube is a globule of mercury and a pair of wires contactable by the mercury. Electrical means are provided for each of the chamber sections for expanding the gas contained therein to move the mercury. Suggested heating means include a heating filament and a heating coil. U.S. Pat. No. 3,632,941 describes a switch comprising a globule of mercury movable within a cavity of substantially uniform cross-sectional area for selectively contacting the ends of a pair of wires by applying fluidic pressure alternately to opposite ends of the globule of mercury from first and second pressure sources. Means utilizing high surface tension of mercury are provided between the chamber in which the mercury moves and pressure sources to prevent the mercury from entering into the pressure sources.
The prior art conductive liquid or fluid switches, operate satisfactorily for their intended uses, but generally are expensive, bulky, slow, and shock, temperature and position sensitive.